Megaconstellations promise a steady flow of de-orbiting debris. Can the sky take it?
Space hardware tumbling out of orbit may lead to unforeseen environmental and climate impacts. Due to the growing scale and pace of launch activities, what is needed is better monitoring of the situation, as well as regulation to create an environmentally sustainable space industry.
Making that case is Jamie Shutler, associate professor of Earth observation at the University of Exeter, Cornwall.
Shutler and colleagues authored the research paper “Atmospheric impacts of the space industry require oversight” in the August issue of the journal Nature Geoscience.
Decreased satellite costs have led to large spacecraft constellations, thereby creating a constant flow of de-orbiting debris as craft die and are replaced. “This debris could double the annual injection of aerosol particle mass into the mesosphere,” the paper explains, thereby increasing the number of aluminum particles that can reach the stratosphere, where they promote ozone loss.
“We are now realizing the full benefits of access to space, but our understanding of the environmental impact of these activities is currently limited,” Shutler told SpaceNews. “Maximizing these benefits whilst minimizing the environmental impact is likely to become increasingly important for science and industry.”
As for research priorities that need to be further explored, Shutler underscored there are key steps forward. One is for the space industry to collect rocket emissions data during launches and make it publicly available.
Shutler said that industry could also make available the total satellite content, a simple total for each type of mineral or substance within their existing spacecraft and satellites yet to be lofted.
“These data would significantly aid research in this area,” Shutler said. “The research itself is going to be highly cross-disciplinary and need input from rocket designers, atmospheric scientists, numerical modelers, satellite and orbital engineers, climate scientists, etc.”
In another study, published in June in the journal Earth’s Future, researchers from University College London (UCL), the University of Cambridge and the Massachusetts Institute of Technology assessed the impact of rocket launches and space debris on stratospheric ozone and global climate.
Eloise Marais, a study co-author and associate professor of physical geography at UCL, said there’s a need for more sustainable solutions for dealing with space debris. Even if a reentering rocket were to completely “burn up,” it would produce the air pollutant nitric oxide (NOx) from the high temperatures, she said, contributing to the depletion of ozone in the stratosphere where ozone protects us from harmful ultraviolet radiation from the sun.
A follow-on study project is underway, said Marais, one that estimates the potential emissions from SpaceX’s Starlink and Starship programs.
While that research is in progress, “certainly our preliminary results suggest that the substantial increase in satellite launches and early return of satellites from the Starlink program are cause for concern,” Marais said.
Adding their view to gauging environmental and other effects on Earth’s atmosphere from satellite reentry is the U.S. Government Accountability Office. GAO’s September report to Congress, “Large Constellations of Satellites: Mitigating Environmental and Other Effects,” observes that spacecraft produce emissions when they make their fiery fall during reentry.
As of spring 2022, there are almost 5,500 active satellites in orbit, the GAO explains, and one estimate predicts the launch of an additional 58,000 by 2030.
Exotic material emissions can be produced during satellite reentry, the GAO study observes, citing experts. Those exotic materials can include paints, resins, epoxies, toxic materials, and radioactive materials used in spacecraft components such as electronics and batteries.
“Rocket launches and satellite reentries produce particles and gases that can affect atmospheric temperatures and deplete the ozone layer. Limiting use of rocket engines that produce certain harmful emissions could mitigate the effects,” states the GAO study. Regarding satellite reentry emissions into the upper atmosphere, GAO found that “the size and significance of these effects are poorly understood due to a lack of observational data, and it is not yet clear if mitigation is warranted.”
Drawing upon a specially convened meeting of experts in coordination with the National Academies in November 2021, the GAO appraisal said that industry cooperation on the makeup of spacecraft would help increase the understanding of how materials react during reentry.
There are few observational data for satellite reentry, the GAO report states, “and accurate modeling data are limited because the industry has not released satellite composition data.”
This article originally appeared in the November 2022 issue of SpaceNews magazine.